1. Field
The disclosed subject matter relates to a vehicle brake disk and a method of manufacturing the same. More specifically, the disclosed subject matter relates to a ventilated brake disk that has variable thickness friction plates and variable vane length and location.
2. Brief Description of the Related Art
Conventional vehicle disk brake rotors are arranged to rotate with a wheel hub of the vehicle. The rotor includes two oppositely-facing annular friction surfaces which, during operation of the brake, are engaged by two blocks of friction material (e.g., brake pads) which are moved (usually by hydraulic or pneumatic devices) towards one another into contact with the two friction surfaces so that frictional forces occur and slow the rotation of the rotor, and hence slow the wheel of the vehicle.
In order to reduce temperature/heat accumulation in disk brake rotors that is caused by the frictional forces, conventional rotors include a first generally annular friction portion which provides one of the annular friction surfaces, and a second generally annular friction portion which provides the other of the annular friction surfaces. The first and second friction portions are conventionally of constant thickness so that they have substantially equal thermal capacity at all points thereof. The friction portions are also arranged in spaced parallel relationship. These friction portions are joined by vanes between which are cooling ducts extending radially and outwardly of the rotor. The cooling ducts are arranged so that, as the rotor is rotated, air passes through the ducts and acts to cool the friction portions. Air inlets to the ducts are provided at an inner edge of the first and second friction portions so that the rotor functions as a centrifugal fan driving air outwardly to outlets at the outer edges of the friction portions.
The most common type of disk brake rotor used on vehicles has first and second friction portions, as described above, and includes an annular mounting portion configured to engage the wheel hub of the vehicle. The rotor includes a generally cylindrical connecting portion which extends axially and joins the annular mounting portion to the first friction portion. The first friction portion is displaced axially relative to the mounting portion and is supported by the connecting portion. The second friction portion is supported by the above-described vanes and is offset from the first friction portion.
Most rotors of the above-described general construction have their first friction portion nearer to the mounting portion than their second friction portion. Thus, there is free access for the cooling air to flow between the inner edges of the first and second friction portions. However, this design is subject to the problem known as “coning”. Coning occurs when the friction portions become hot and expand while the connecting portion, which is not so hot, expands less. Thus, the connecting portion is pulled into a slightly conical form by the first friction portion. Expansion of the second friction portion can enhance this effect. This results in the friction portions bending out of their initial planes. This bending causes points of concentration of pressure to occur during braking at certain locations of the friction portion, which generates heat at these locations. These higher heat locations have to absorb greater amounts of heat than other portions of the friction portions. This causes temperature differentials which affect the performance of the brake and also affect the wear of the rotor and the brake pads. The temperature and pressure differentials can also result in cracking or other deterioration of the rotor.
High heat loads that occur in a brake disk while bringing a vehicle to a stop can also cause brake disk deformation, stress, and cracking due to the in appropriate thermal expansion of the disk. For example, brake disk deformation due to heat load can cause uneven brake pad wear, and uneven brake pad wear can reduce a brake's general effectiveness. Moreover, as taper wear increases, the vehicle stopping distance will increase for the same pedal input stroke. Uneven brake pad wear also causes higher brake drag, which results in lower fuel efficiency and higher brake judder. Thus, there has been a long felt need in the art to achieve solutions to the above-described and other problems in the field of vehicle brakes.